The present invention relates to an imaging system for a document reproduction device which utilizes a linear lens array in an optical system to transmit an image of a document to an object plane to an image plane through a magnification range. More particularly, the invention relates to an imaging system which utilizes a moving document, a scanning lens array and a moving photoreceptor in a unique set of velocity relationships.
Document reproduction systems utilizing linear lens arrays imaging systems are known to the art in two principal embodiments. U.S. Pat. No. 3,544,190 is representative of these systems which utilize a linear stacked array of lenslets known as "strip lenses". U.S. Pat. No. 3,977,777 is representative of those scanning systems utilizing a scanning lens array comprising bundled gradient index optical fibers. Both these latter imaging systems are desirable for use in document reproduction machines because they transmit an erect image at an imaging plane, have a short total conjugate and greatly reduce the mass and expense associated with the conventional lens, multi-mirror scan systems. Gradient index lens arrays have especially found wide acceptance as replacements for conventional image transmitting components in copiers as disclosed, for example, in U.S. Pat. Nos. 3,947,106 and 3,977,777. Each of these prior art copiers uses a single gradient index lens array to transmit images at a magnification of 1:1. And each of these imaging systems utilizes a fixed lens system, scanning being accomplished by moving the document past the lens in conjunction with a similar motion of a photoconductive imaging plane.
These systems, which can be characterized as "moving platen" systems, impose constraints on equipment size since the platen must travel the width of a document during the scan cycle.
Other scanning systems are known which accomplish the scanning function by moving a linear lens array beneath a fixed document. Illustrative of such systems are the scanning systems disclosed in U.S. Pat. No. 4,129,373 (FIG. 1) and Japanese Publication No. 55-1206.
A third possibility exists wherein the document, photoconductive imaging plane and linear lens array all move at speeds bearing a certain relationship to each other. This type of system, as disclosed in Japanese Publications Nos. 53-97436 and 55-52074 and U.S. Pat. No. 3,754,822 (Melrose) has the desirable characteristics of compactness coupled with increases in process speed.
All of the above-disclosed systems are related to imaging systems which transmit images at unity (1X) magnification. To enable a multi-magnification copier utilizing a linear lens array, a variety of problems are present which have heretofore not been completely resolved. One example of utilizing a linear lens array in a multi-magnification mode system is disclosed in copending U.S. application Ser. No. 151,994, published as European Publication No. 0040548 on Nov. 25, 1981, assigned to the same assignee as the present invention. In this application various reproduction systems are disclosed which utilize a gradient index lens array as the imaging device. One embodiment discloses a lens assembly consisting of a 1X array coupled with a reduction/enlargement lens array, the latter constructed according to the principles disclosed in said application. This system utilizes a moving platen and fixed lens array, the platen to photoreceptor speed changing during magnification changes to maintain proper image exposure at the photoreceptor.
It is desirable to improve throughput at the same process speed and reduce the size of this type of multi-magnification system, as well as other systems employing linear lenses in a multi-magnification copying device. The present invention is therefore directed to an imaging system for projecting an erect image of a document lying in an object plane onto a photoreceptor lying in an image plane and at a plurality of magnifications, said system including:
an imaging assembly positioned between said object plane and photoreceptor, PA1 a drive arrangement for moving said document, photoreceptor and imaging assembly in a unity magnification scanning mode, said arrangement comprising: PA1 first drive means for driving said photoreceptor in a first direction at a first velocity v, PA1 second drive means for driving said document in said first direction at a velocity v' where v'=v, and PA1 third drive means driving said imaging assembly at a third velocity v" in a second direction opposite to the said first direction, PA1 said drive arrangement further adapted to move said document, photoreceptor and imaging assembly in a non-unity magnification mode such that said first, second and third velocities are related by the expression: ##EQU1##
An additional feature of the above system is the added advantage of enabling the scanning system in a precession scanning mode. As described in copending Application Ser. No. 190,160, assigned to the same assignee as the present invention, the scanning of a document is accomplished at a faster rate than the process speed so as to cause the image at the image plane to be precessed, or moved, along the image plane in a direction opposite to the movement of the image plane. A major advantage of any precession system is that it can reduce throughput time by using the process distance gained during the precession activity to accomplish a specific time consuming activity such as placing a new document on the platen and/or returning the scan system to a start-of-scan position.